1. Field of the Invention
The present invention relates to a progressive-addition lens having a progressive surface as one surface and an aspherical or atoroidal surface as the other surface and to a method for preparing shape data thereof. In addition, the present invention relates to a method for manufacturing such a progressive-addition lens, an apparatus for preparing the shape data, and a computer program product for preparing the shape data.
2. Description Related Art
A progressive-addition lens having a portion with power for distance viewing and a portion with power for near viewing, where dioptric power is continuously changed from one portion to the other portion, has been developed. The progressive-addition lens is mainly used as a lens for far-sighted spectacles and is apparently indistinguishable from typical far-sighted spectacles, while having an advantage that clear vision can be continuously obtained from a distance to a hand. In recent years, therefore, the progressive-addition lenses have been widely used in general.
The surface configuration of the progressive-addition lens includes a progressive surface on an object-side surface (front surface) and a spherical or toroidal surface (astigmatic surface) on an eye-side surface (back surface). Alternatively, another surface configuration of the progressive-addition lens has been known in the art, where a spherical surface is arranged on the object-side surface (front surface), and a progressive surface or a synthetic surface of a progressive surface with a toroidal surface is arranged on the eye-side surface (back surface). In addition, there is proposed that the spherical or toroidal surface formed on one of the surfaces is constructed of an aspherical or atoroidal surface to carry out aberration correction based on prescribed power (e.g., correction of astigmatism, field curvature, or distortion aberration) in a region on the periphery side of the lens (see, for example, Patent Documents 1 and 2).
Furthermore, in the present specification, the curved surface which is a portion of a rotation surface having a rotation axis and in which the curvature continuously changes from the intersection with the rotation axis to the periphery is referred to as an aspherical surface. The curved surface which has a principal meridian showing maximum curvature and a principal meridian showing minimum curvature and which is a part of a line-symmetric curved surface with respect to a normal line at the intersection of the principal meridians as a symmetric axis and in which the curvature of one of the principal meridians continuously changes toward the outside from the intersection with the other principal meridian is referred to as an atoroidal surface. Also, a progressive-addition lens provided with a progressive surface only on one side is referred to as a one-side progressive-addition lens. In addition, the other side of the one-side progressive-addition lens, which is opposite to the progressive surface and which is formed of a spherical or toroidal surface is also referred to as a spherically designed surface, and the surface formed of an aspherical or atoroidal surface is also referred to as an aspherically designed surface. In addition, the one-side progressive-addition lens having a spherically designed surface on the side opposite to the progressive surface may be referred to as a spherically designed one-side progressive-addition lens, while one having an aspherically designed surface is referred to as an aspherically designed one-side progressive-addition lens.
In particular, the aspherically designed one-side progressive-addition lens can be provided with corrected astigmatism on the lens periphery side to improve the optical characteristics thereof that act on the eye, while the thickness of the lens can be reduced.    [Patent Document 1] National Publication of International Patent Application No. 1995-504769    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 57-10112